1. Field of the Invention
The present invention relates to a cable assembly including a differential signal transmission cable that includes a pair of signal conductors and transmits a differential signal composed of signals having phases that are inverted by 180 degrees with respect to each other, and to a method of manufacturing the same.
2. Description of the Related Art
In known apparatuses such as servers, routers, and storages that handle high-speed digital signals at several Gbit/s or higher, differential interface standards such as low-voltage differential signals (LVDS) are employed, and differential signals are transmitted via differential signal transmission cables between apparatuses or between circuit boards included in each apparatus. A differential signal is characterized in having high resistance to exogenous noise while reducing the voltage of the system power source.
The differential signal transmission cable includes a pair of signal conductors, to which a positive signal and a negative signal having phases that are inverted by 180 degrees with respect to each other are transmitted, respectively. The potential difference between the two signals (the positive signal and the negative signal) corresponds to the signal level, which is identified on the receiver side. For example, if the potential difference is positive, the signal level is “high”; if the potential difference is negative, the signal level is “low”.
A technology concerning a differential signal transmission cable that transmits such a differential signal is disclosed by Japanese Unexamined Patent Application Publication No. 2012-099434 (FIGS. 1 and 2), for example. The differential signal transmission cable disclosed by Japanese Unexamined Patent Application Publication No. 2012-099434 includes a pair of signal conductors that are arranged parallel to each other with a predetermined gap interposed therebetween. The signal conductors are covered with an insulator. Specifically, the signal conductors are held by an insulator in such a manner as to be parallel to each other with a predetermined gap interposed therebetween. The insulator is covered with a sheet-type outer conductor. The outer conductor is covered with a sheath (protective covering).
One end of the differential signal transmission cable is stripped stepwise, whereby portions of the signal conductors and a portion of the outer conductor are exposed to the outside. A shield connection terminal made of metal is connected to the exposed portion of the outer conductor by caulking. The shield connection terminal includes a sheet metal and a soldered connection pin that is integrally formed on the sheet metal. When caulking is performed, the sheet metal undergoes plastic deformation in such a manner as to conform to the shape of the outer conductor. Hence, the outer conductor and the shield connection terminal are electrically connected to each other, allowing electrical connection between the outer conductor and a ground pad of a circuit board via the shield connection terminal (the sheet metal and the soldered connection pin).
In the technology disclosed by Japanese Unexamined Patent Application Publication No. 2012-099434 (FIGS. 1 and 2), a soldering bit used in soldering work and heated to about 350° C. does not touch the outer conductor, unlike a case where the outer conductor is directly soldered to the ground pad. Therefore, the occurrence of deformation or melting of the insulator due to the heat of the soldering bit is suppressed. Nevertheless, since the shield connection terminal is caulked in such a manner as to conform to the shape of the outer conductor, the insulator provided on the inner side of the outer conductor may be elastically deformed by the caulking force, leading to manufacturing problems such as a change in the distance between the signal conductors provided on the inner side of the insulator. Consequently, electric characteristics of finished differential signal transmission cables may vary.